What Does "Sterling" Mean?
Think of the necklace or earrings you're wearing as 1000 parts metal. If at least 925 of those 1000 parts are pure silver then the item is classified as "sterling". The other 75 parts are another metal, often copper, zinc, germanium, or a combination of metals.
Sterling silver is considered superior to non-sterling because of its value and quality. Sterling silver jewelry can have up to about 975 parts silver but jewelry with a silver content of over 975 is harder to find, as it tends to be softer and not sufficiently durable for regular wear.
How Do I Care For My Jewelry?
The best way to prevent sterling silver from tarnishing is to keep it covered when not in use, ideally in a plastic bag or wrapper. Bubble wrap, Ziploc bags, cellophane all work great. Tarnishing (oxidization) of sterling silver is from outside elements reacting to the silver, so keeping it covered with the air squeezed out is the best way to keep it shiny.
Should any of your sterling silver tarnish, or if it just looks dull and you want to get it shiny again, you can use this trick that I learned from my silversmiths:
Line a bowl with aluminum foil. Add water and some kind of good quality cleaning (dish or laundry) detergent such as Tide, Wisk, Seventh Generation, Dawn, etc. Stir to get the mixture foamy. Just be sure that the detergent doesn't contain bleach, Febreze or any other "extras". Soak your sterling silver for 1/2 hour up to several hours. Take it out and gently scrub it with soft toothbrush or towel then rinse with water & gently pat dry. Now and then I have some pieces that need to be brightened up and this has always worked well for me.